A liquid crystal cell which performs light modulation with use of optical rotatory property and birefringence in liquid crystal molecules is combined with a polarizing plate (including a polarizing film). The polarizing plate decomposes the incident non-polarized light to two polarized light components which are perpendicular to each other. Further the polarizing plate blocks light of the polarized light component parallel to an absorption axis, and transmits light of the polarized light component perpendicular to the absorption axis. In a transmissive liquid crystal cell, the polarizing plates are disposed at both a light incident surface side and a light exit surface side of the liquid crystal cell. The absorption axes of the polarizing plates are directed perpendicular to each other. The polarizing plate in the light incident surface side functions as the polarizer which converts non-polarized light to specific linearly polarized light and allows the specific linearly polarized light to enter the liquid crystal cell. The polarizing plate in the light exit surface side functions as an analyzer which blocks or transmits modulated light from the liquid crystal cell according to a polarization direction of the modulated light.
The polarizing plates are respectively disposed in front of and at the back of, for example, a TN (Twisted Nematic) liquid crystal cell in a cross-nicol in which absorption axes of the polarizing plate are perpendicular to each other, thus resulting in a liquid crystal display in a normally white mode. The TN liquid crystal cell has rod-shaped liquid crystal molecules filled between a pair of transparent substrates on which transparent electrodes and alignment films are formed. The liquid crystal molecules constitute a liquid crystal layer. When no voltage is applied between the pair of substrates, that is in a normal state, long axes of the liquid crystal molecules are kept approximately parallel to the substrates. The molecules are rotated gradually in a thickness direction of the liquid crystal layer so that the long axes of the liquid crystal molecules twist by 90 degrees as a whole along with the orientation of each of the liquid crystal molecules.
The polarizing plate is originally constructed for absorbing light whose polarization plane is parallel to an absorption axis of the polarizing plate and transmitting light perpendicular to the absorption axis of the polarizing plate among light entering the polarizing plate. As a result, a polarization plane of polarized light having occurred upon entering the polarizing plate in a direction of a normal line of the polarizing plate is not always parallel to a polarization plane of polarized light having occurred upon entering the polarizing plate in a direction inclined with respect to the normal line. That is, since the polarization plane changes depending on the incident azimuth with respect to the polarizing plate, a light extinction ratio in a cross-nicol also depends on the incident angle, thus resulting in a so-called viewing angle dependency. Accordingly, there causes one of reasons for impossibility of achieving a preferable light extinction ratio. It is noted that, the viewing angle dependency may result from the orientation of the liquid crystal itself, which is not related with the present invention.
As disclosed in Japanese Patent Laid-open Publication No. 2001-350022 and the like, two biaxial phase difference plates are laminated on one polarizing plate (polarizer) so that slow-phase axes thereof are perpendicular to each other therebetween. Accordingly, inclination of the polarization plane of linearly polarized light having passed through the polarizing plate is compensated. As a result, the polarization plane of the linearly polarized light having occurred upon entering the polarizing plate in a direction inclined with respect to the direction of the normal line is aligned with linearly polarized light having occurred upon entering the polarizing plate in the direction of the normal line, thus making it possible to prevent leakage of light from the other polarizing plate (analyzer).
TFT (Thin Film Transistor)-LCD causes a transistor to control turning on and off of a voltage to be applied to an area corresponding to one pixel of the liquid crystal layer. Therefore, the switching between on and off for each pixel is conducted fast and accurately. As a result, the TFT-LCD is used widely for a display requiring high image quality. The TFT-LCD includes a TFT substrate on which a TFT array, a wiring pattern of the TFT array, and a transparent pixel electrode are formed, and a opposed substrate on which a common electrode corresponding to the pixel electrode of the TFT substrate is formed.
The TFT substrate and the opposed substrate consist of a transparent glass substrate, for example. In the liquid crystal projector, the TFT substrate is disposed at a project lens side. The opposed substrate is disposed at a light source side. On the opposed substrate, in order to prevent malfunction due to strong light applied to the TFT, is formed a black matrix (light shielding layer) arranged in a matrix fashion for protecting the TFT from light. Additionally, in order to prevent loss of light due to the black matrix, a microlens array is disposed on the opposed substrate so that light emanated from the light source is condensed for each pixel, and light passes through an opening of the black matrix.
However, a panel size of the TFT-LCD for use in the liquid crystal projector is smaller than that of the TFT-LCD for use in a direct-view type display. Therefore, in order to project a high-resolution image on a screen, the pixel density becomes considerably high, and a microlens array, a TFT array, and a black matrix are arranged with a pitch of approximately 10 μm. Accordingly, a structure having periodic microstructures, such as the microlens array, the TFT array, the black matrix, and the like allows part of incident light to diffract, thereby causing a phenomenon in which predetermined incident light diffuses by approximately 10 degrees at one time, and in total, 20 to 30 degrees. As a result, there arises a problem in which when part of light having passed through the incident-side polarizing plate passes through the exit-side polarizing plate, its incident angle on the latter is varied to cause leakage of light from the exit-side polarizing plate. This problem occurs in addition to the problem of viewing angle dependency of the polarizing plate based on the azimuth angle of incidence described above, thus making it difficult to solve both problems.
A primary object of the present invention is to provide a liquid crystal display and a liquid crystal projector capable of compensating displacement of a polarization plane due to a viewing angle dependency of a polarizing plate and compensating diffraction due to a structure of a liquid crystal cell.
Another object of the present invention is to provide a liquid crystal display and a liquid crystal projector capable of displaying an image of high contrast without causing brightness unevenness by preventing leakage of light in a wide viewing angle, independent from the operation mode of the liquid crystal.